1. Field of the Invention:
This invention relates to a process for producing a block copolymer composed of polyphenylene sulfide (to be abbreviated as PPS hereinafter) segments and polyphenylene sulfide sulfone segments, and a composition comprising the block copolymer. More specifically, this invention relates to process for producing a block copolymer by chemically bonding an aromatic sulfide sulfone polymer as soft segments to PPS. The block copolymer is improved in mechanical properties having to do with toughness, such as impact strength and pliability, and can be used as various molding materials. The invention also pertains to a composition comprising the block copolymer.
2. Description of the Related Art:
PPS has attracted attention as high performance engineering plastics having outstanding heat resistance, chemical resistance and rigidity over ordinary engineering plastics such as nylon, polycarbonate, polybutylene terephthalate and polyacetal. The PPS resin, however, has the serious defect that it has low toughness and is fragile as compared with the ordinary engineering plastics. In recent years, linear PPS different from the conventional heat-crosslinked PPS has been developed, but in the crystallized state, it has poor toughness characteristics such as low impact strength and elongation.
In order to improve the impact strength of PPS, it has been the previous practice to incorporate a filler such as glass fibers. But since this method does not bring about a sufficient result, it is not effective for the prevention of cracking owing to molding shrinkage strains.
On the other hand, preparation of a polymer blend of PPS with a flexible polymer is an effective method. But since there are few polymers which are flexible and have excellent heat resistance and chemical resistance or the compatibility of the flexible polymer with PPS is insufficient, problems arise such as the reduction of mechanical strength (flexural strength, etc.) and the deterioration of the surface condition of the molded articles. No PPS has yet been obtained which has improved impact strength and flexibility without impairing the inherent characteristics of the PPS resin.
In view of the foregoing state of art, the present inventors have made extensive investigations in order to obtain a PPS resin having improved mechanical properties such as improved impact strength and excellent blending compatibility, and have consequently found that a block copolymer resin obtained by copolymerizing PPS and PPSS to bond them chemically is an effective resin having these desirable properties.